Coloring and hardening steel



March 9, 1937. A. R. STARGARDTER COLORING AND HARDENING STEEL Filed0018, 1932 ZZZ? 7 7763 Patented Mar. 9, 1937 UNITED PATENT OFFICECOLORING AND HABDENING STEEL Application ()ctober 8,

This invention relates to the treatment of steel in producing hardenedand tempered articles with blued or other colored surface finish. In oneaspect it consists in a novel method characterized by the step ofsubjecting the heated steel to the oxidizing action of the products ofcombustion of an air gas mixture of controlled composition while thesteel is heated to its critical point preparatory to the hardening step.In another 1 aspect it consists in novel apparatus herein shown asadapted for use in practicing such method. While my invention is ofgeneral application, it has a particular held of use in the treatment ofstrip steel, such, for example, as that employed in the manufacture ofsafety razor blades, and it is herein disclosed as it is carried out inthat field.

It will be understood that when steel is heated to temperatures aboveits lower critical point in preparation for hardening and while incontact with the atmosphere or a medium having an oxidizing efiect equalto or greater than the atmosphere, the surface of the steel is oxidizedfar beyond the blue color, becoming gray and also it is inclined toscale.

I have discovered that by limiting and controlling the oxidizing efiectof the atmosphere or gas mixture surrounding the steel while the latteris heated above its critical point, preparatory to hardening, a bluedfinish may be imparted to the steel independently of its hardness ortemper. By varying the oxidizing effect of the gas mixture in contactwith the steel, the color of its finish may be varied as desired andblue or other colors secured. It is thus possible to produce steelarticles of any desired degree of hardness having a surface finish ofany color desired and bearing no predetermined relation to the hardnessof the steel. For example: I may impart a clued finish to glass-hardsteel, or to steel of a hardness corresponding, in the ordinary drawingprocess, to straw color. In other words, by my invention I am enabled toproduce a colored steel of any desired degree of hardness having anydesired surface color merely by modifying the conditions under which theusual step of heating the steel preparatory to hardening is carried out.

In my prior Patent No. 1,948,192 granted February 20, 1934, I havedisclosed and claimed a method of treating steel of this generalcharacter and adapted particularly to be carried out in connection witha gas-fired furnace. The method of the present invention is adapted tobe carried 55 out in connection with such furnaces or with 1932, SerialNo. $36,823

furnaces heated by any other method and any form of heat in-put. it isalso adapted to the successful treatment of certain grades of steelwhich have not heretofore been treated with entire success by the methodof my earlier patent, since by means of the present invention a closerand more discerning control is attainable.

One gas mixture suitable for carrying out the method of the presentinvention is the product of the combustion of air and illuminating gas,mixed in proper proportion and burned out of contact with steel to betreated. Such products of combustion have an oxidizing efiect upon thesteel which is less than that of atmospheric oxygen so that when thesteel is heated to or above its critical point in the presence of thisgas, a limited surface oxidation takes place and this may be restrictedto that corresponding to a blue or other color. In carrying out themethod of my invention, the products of combustion thus prepared arecaused to flow along the strip steel while the latter is being fedthrough a zone in which it is heated to a temperature above its lowercritical point. The strip is accordingly colored by oxidation at thesame time and in the same heat by which it is prepared for hardemng.

While the method of my invention is not limited to any specificapparatus, I have herein shown one example of a construction whichpossesses certain advantages when employed in carrying out the method.This apparatus consists in a fitting providing a chamber in which thestrip to be treated and the gas mixture are first brought into contactwith each other and from which they are simultaneously advanced to themufiie or other member defining the heated zone.

The nature of my invention will be best understood and appreciated fromthe following description of one manner in which it may be carried outin connection with the novel apparatus shown in the accompanyingdrawing, in which:

Fig. 1 is a. plan view of the apparatus, certain portions thereof beingbroken away to expose the path of the steel strip;

Fig. 2 is a corresponding view in front elevation;

Fig. 3 is a view in longitudinal section on an enlarged scale of themixing chamber and burner; and

Fig. 4 is a view in cross-section on the lines 4-4 of Fig. 3.

As shown in the drawing, the apparatus is supported at convenient heightupon a bench or 2 frame ln which is provided at one end with a bracketl2 for the supply reel 14 from which the strip steel is drawn and at theother end with a bracket I6 for the receiving reel l8 upon which thetreated strip -steel is rewound. The steel strip is advanced through theapparatus under tension by a pair of feed rolls 20 which are arranged tobe driven at appropriate speed by means not herein shown. In passingfrom the supply reel I 4 to the receiving reel l8, the steel strip isguided in a straight line path successively through a gas chamber 22, aheater 32, chilling plates 62 and a drawing heater 64. These are mountedin a straight line upon the surface of the bench or frame l0 andadjacent to each other, so that the strip may pass without interruptiondirectly from one to the next in the series.

The gas chamber 22 comprises a T-shaped fitting having an inclinedinterior partition or'wall 24 located midway between its ends andprovided with a slit which constitutes an inlet port for the passage ofthe steel strip I5. The side inlet of the fitting is directed rearwardlyand interiorly threaded for connection with the combustion chamber 38.The inner end of the T fitting is exteriorly threaded to receive thecoupling 28 which serves as the connecting medium between the gaschamber and an elongated muflle 38 of the heater 32. The muiile 38 ofthe heater 32 is maintained by any suitable medium, such as gas orelectricity, at a temperature above the lower critical point of thesteel being treated, for example above 1400 F. and the strip steel isheated to that temperature in its passage through the mufile.

The inlet 26 of the gas chamber or receiver is connected through a union34 and nipple 36 with the lower end of the combustion chamber 38. Thischamber 38 has a square bottom 40, into which the nipple 36 is threaded,and a square top 42 perforated to receive a burner 50 which will bepresently described. The side walls of the combustion chamber arerectangular and it has an interior flue which is formed by a pair ofelongated porcelain shells or sleeves 46 rectangular in cross-section asshown in Fig. 4 and arranged end to end between the ends 42 and 40 ofthe combustion chamber. The space between the outer side walls of thecombustion chamber and the shells 46 is filled with refractoryheat-insulating material such as asbestos in which may be embeddedspacing members 45. The shells 46 are exteriorly threaded and wound inthe threads thereof is resistance wire 48 by which the combustionchamber may be maintained at a temperature above the ignition point ofthe gas mixture to be burned.

The burner or mixing nozzle 50 is provided with a reduced outlet whichextends through the inlet end 42 of the combustion chamber. The outerend of the mixing nozzle is closed by a perforated plug 52 into which isthreaded the end of a gas pipe 54. The periphery of the burner isperforated by air inlet ports 55 and provided with a circumferentialchannel for a perforated ring 56, by turning which the eifective area ofthe air inlet ports may be adjusted. The contacting ends of the shells46 are notched to form an opening midway of the inside of the mixingchamber and with this communicates a laterally-extending sleeve 58forming an outlet passage. The outer end of the sleeve 58 is closed, orpartially closed, by a slidable damper 60 and in this manner the amountof burning gas escaping from the mixing chamber may be regulatedindependently of the combustible mixture delivered to the flue by theburner 58. The combustible mixture supplied by the burner is ignited andburns with a flame extending inwardly into the mixing chamber. Theproducts of this combustion are further heated in the chamber which ismaintained at an elevated temperature by the resistance wires 48 andthen the hot products of combustion are discharged through the nipple 36and proceed into the mufile 30 via the receiver 22.

In carrying out the method of my invention with the apparatus hereinillustrated, illuminating gas is supplied to the burner 50 and deliveredto the outer end of the combustion chamber 38, inspirating with it aregulated'amount of air through the ports 55. The interior of thecombustion chamber is maintained at a temperature above the ignitionpoint of the gas so that the latter is immediately ignited upon leavingthe burner and burned with a flame which may completely fill the chamberand pass into the nipple 36. The products of combustion pass out of theouter end of the combustion chamber through the union 34 and enter theintermediate or gas chamber 22. The pressure of the gas thus deliveredand its composition are controlled to some extent by opening or closingthe ports 55 and also the damper 60 in the upper side of the combustionchamber. The gaseous products of combustion are delivered directly uponthe steel strip l5 which is led into the muille 30 through a narrow slitin the partition 24. The current of the hot products of combustion isdefiected by this partition towards the furnace 32 and fiows with thestrip l5 through a slit or orifice in the end of the muiile 30,enveloping the strip in its passage through the heated muflie, where thesteel strip is maintained at a temperature above its lower criticalpoint, as, for example 1400 F.

It will be noted that the strip and the gaseous products of combustionare first brought together in the gas chamber 22 and then simultaneouslyadvanced or delivered from this to the receiving end of the mufile 30.In its passage through the muflie, the steel strip I5 is oxidized by thehot products of combustion in the manner above explained. The strip thuscolored passes directly from the furnace 32 to chilling plates 62,preferably water-cooled and effective to harden the strip continuouslyas it is moved between them. The hardened and blued strip next passes tothe drawing furnace 64 which is heated to a temperature appropriate todraw the temper of the steel strip from the very hard condition in whichit leaves the chilling plates 62 to the temper best suited for thepurposes for which the strip steel is intended.

It will be observed that the feeding rolls 20 maintain the strip I 5under tension in passing from the supply reel l4, retaining it in asmooth fiat condition during the steps of heating and oxidizing in thefurnace 32. Treatment of the steel in this condition contributes to theformation of a smooth, continuous and homogeneous surface finish.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:--

1. The method of hardening and coloring steel, which consists in heatingthe steel to a temperature above its lower critical point, burning anair-gas mixture out of contact with the steel and controlling theresulting products of combustion so that they have a predeterminedoxidizing effect which is less than atmospheric, leading said productsof combustion in a current contacting the heated steel, and thenchilling the steel and thereby producing a hardened and colored product.

2. The method of hardening and coloring steel, which consists in burningan air-gas mixture in a closed chamber out of contact with the steel andcontrolling the resulting products so that they have a predeterminedoxidizing effect which is less than atmospheric, leading said productsof combustion to the steel and flowing them in a current along thesurface of the steel while the latter is heated above its criticalpoint, thereby oxidizing the same to a limited degree, and then chillingthe steel to produce in one operation a hardened and colored product.

3. The method of hardening and coloring strip steel, which consists inadvancing the strip through a heated muflle, burning an air-gas mixtureoutside the muiiie and controlling the resulting products of combustionso that they have a predetermined oxidizing efiect which is less thanatmospheric, leading the products of combustion to the steel in a pathdisposed at an angle to the direction of movement of the strip in themuflie, causing said products of combustion to envelop said strip whilethe latter is heated above its critical point and to oxidize the surfacethereof,

to a temperature above the critical point of the steel, flowing intocontact with the strip in the heated zone the products of combustion ofan air-gas mixture of controlled composition having a predeterminedoxidizing effect less than atmospheric, the major portion whereof beingburned out of contact with the strip, and then chilling the strip toproduce at a single operation a hardened and blued steel strip.

5. The method of continuously hardening and blueing strip steel, whichconsists in drawing the strip through an elongated muiile heated to atemperature above the critical point of the steel, burning outside themuffle an air-gas mixture of controlled composition to produce productsof combustion of a predetermined oxidizing eflect which is less thanatmospheric, conducting said products of combustion into contact withthe surface of the strip while the latter is maintained by the muflle ata temperature above the critical point of its steel, and thenprogressively chilling the strip immediately upon leaving the mume toproduce a hardened and blued product.

6. The method of continuously hardening and blueing strip steel, whichconsists in feeding the strip through a zone heated to a temperatureabove the critical point of the steel, and as the strip enters saidzone, admitting thereto, through a restricted orifice and at relativelyhigh velocity, gaseous products of combustion having an oxidizing effectless than that of atmospheric oxygen, and subsequently chilling thestrip and thereby producing a hardened and blued strip.

ALBERT R. STARGARDTER.

